Method and apparatus for supporting UE-to-network relay communication in a wireless communication system

ABSTRACT

A method and device are disclosed from the perspective of a remote UE. In one embodiment, the method includes the remote UE establishing a first unicast link with a relay UE. The method also includes the remote UE establishing a Radio Resource Control (RRC) connection with a network node via the relay UE. The method further includes the remote UE establishing a second unicast link with a second UE. In addition, the method includes the remote UE detecting a sidelink radio link failure. Furthermore, the method includes the remote UE initiating or performing a RRC connection re-establishment procedure if the sidelink radio link failure occurs on the first unicast link. The method also includes the remote UE initiating or performing a Sidelink UE Information procedure if the sidelink radio link failure occurs on the second unicast link.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application claims the benefit of U.S. Provisional PatentApplication Ser. No. 63/272,078 filed on Oct. 26, 2021, the entiredisclosure of which is incorporated herein in its entirety by reference.

FIELD

This disclosure generally relates to wireless communication networks,and more particularly, to a method and apparatus for supportingUE-to-network relay communication in a wireless communication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of datato and from mobile communication devices, traditional mobile voicecommunication networks are evolving into networks that communicate withInternet Protocol (IP) data packets. Such IP data packet communicationcan provide users of mobile communication devices with voice over IP,multimedia, multicast and on-demand communication services.

An exemplary network structure is an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN). The E-UTRAN system can provide high datathroughput in order to realize the above-noted voice over IP andmultimedia services. A new radio technology for the next generation(e.g., 5G) is currently being discussed by the 3GPP standardsorganization. Accordingly, changes to the current body of 3GPP standardare currently being submitted and considered to evolve and finalize the3GPP standard.

SUMMARY

A method and device are disclosed from the perspective of a remote UE.In one embodiment, the method includes the remote UE establishing afirst unicast link with a relay UE. The method also includes the remoteUE establishing a Radio Resource Control (RRC) connection with a networknode via the relay UE. The method further includes the remote UEestablishing a second unicast link with a second UE. In addition, themethod includes the remote UE detecting a sidelink radio link failure.Furthermore, the method includes the remote UE initiating or performinga RRC connection re-establishment procedure if the sidelink radio linkfailure occurs on the first unicast link. The method also includes theremote UE initiating or performing a Sidelink UE Information procedureif the sidelink radio link failure occurs on the second unicast link.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according toone exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as accessnetwork) and a receiver system (also known as user equipment or UE)according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system accordingto one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3according to one exemplary embodiment.

FIG. 5 is a reproduction of FIG. 4.2.7.2-1 of 3GPP TS 23.304 V17.0.0.

FIG. 6 is a reproduction of FIG. 6.1.1.7.2-1 of 3GPP TS 23.304 V17.0.0.

FIG. 7 is a reproduction of FIG. 6.1.2.3.2-1 of 3GPP TS 23.304 V17.0.0.

FIG. 8 is a reproduction of FIG. 6.4.3.1-1 of 3GPP TS 23.304 V17.0.0.

FIG. 9 is a reproduction of FIG. 5.3.3.1-1 of 3GPP TS 38.331 V16.6.0.

FIG. 10 is a reproduction of FIG. 5.3.7.1-1 of 3GPP TS 38.331 V16.6.0.

FIG. 11 is a reproduction of FIG. 5.8.3.1-1 of 3GPP TS 38.331 V16.6.0.

FIG. 12 is a reproduction of FIG. 5.8.9.1.1-1 of 3GPP TS 38.331 V16.6.0.

FIG. 13 is a flow chart according to one exemplary embodiment.

FIG. 14 is a flow chart according to one exemplary embodiment.

FIG. 15 is a flow chart according to one exemplary embodiment.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described belowemploy a wireless communication system, supporting a broadcast service.Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiple access (OFDMA),3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A orLTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra MobileBroadband), WiMax, 3GPP NR (New Radio), or some other modulationtechniques.

In particular, the exemplary wireless communication systems and devicesdescribed below may be designed to support one or more standards such asthe standard offered by a consortium named “3rd Generation PartnershipProject” referred to herein as 3GPP, including: TS 23.304 V17.0.0,“Proximity based Services (ProSe) in the 5G System (5GS) (Release 17)”;TS 38.331 v16.6.0, “NR; Radio Resource Control (RRC) protocolspecification (Release 16)”; and 3GPP email discussion[Post115-e][603][Relay] Relaying CR to 38.331 (Huawei), “Draft_38331Running CR for SL relay_v14_rapp.docx”. The standards and documentslisted above are hereby expressly incorporated by reference in theirentirety.

FIG. 1 shows a multiple access wireless communication system accordingto one embodiment of the invention. An access network 100 (AN) includesmultiple antenna groups, one including 104 and 106, another including108 and 110, and an additional including 112 and 114. In FIG. 1 , onlytwo antennas are shown for each antenna group, however, more or fewerantennas may be utilized for each antenna group. Access terminal 116(AT) is in communication with antennas 112 and 114, where antennas 112and 114 transmit information to access terminal 116 over forward link120 and receive information from access terminal 116 over reverse link118. Access terminal (AT) 122 is in communication with antennas 106 and108, where antennas 106 and 108 transmit information to access terminal(AT) 122 over forward link 126 and receive information from accessterminal (AT) 122 over reverse link 124. In a FDD system, communicationlinks 118, 120, 124 and 126 may use different frequency forcommunication. For example, forward link 120 may use a differentfrequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access network. Inthe embodiment, antenna groups each are designed to communicate toaccess terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmittingantennas of access network 100 may utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals 116 and 122. Also, an access network using beamformingto transmit to access terminals scattered randomly through its coveragecauses less interference to access terminals in neighboring cells thanan access network transmitting through a single antenna to all itsaccess terminals.

An access network (AN) may be a fixed station or base station used forcommunicating with the terminals and may also be referred to as anaccess point, a Node B, a base station, an enhanced base station, anevolved Node B (eNB), a network node, a network, or some otherterminology. An access terminal (AT) may also be called user equipment(UE), a wireless communication device, terminal, access terminal or someother terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmittersystem 210 (also known as the access network) and a receiver system 250(also known as access terminal (AT) or user equipment (UE)) in a MIMOsystem 200. At the transmitter system 210, traffic data for a number ofdata streams is provided from a data source 212 to a transmit (TX) dataprocessor 214.

In one embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna 252 is provided to a respective receiver (RCVR) 254 a through254 r. Each receiver 254 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 is complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use(discussed below). Processor 270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

Turning to FIG. 3 , this figure shows an alternative simplifiedfunctional block diagram of a communication device according to oneembodiment of the invention. As shown in FIG. 3 , the communicationdevice 300 in a wireless communication system can be utilized forrealizing the UEs (or ATs) 116 and 122 in FIG. 1 or the base station (orAN) 100 in FIG. 1 , and the wireless communications system is preferablythe NR system. The communication device 300 may include an input device302, an output device 304, a control circuit 306, a central processingunit (CPU) 308, a memory 310, a program code 312, and a transceiver 314.The control circuit 306 executes the program code 312 in the memory 310through the CPU 308, thereby controlling an operation of thecommunications device 300. The communications device 300 can receivesignals input by a user through the input device 302, such as a keyboardor keypad, and can output images and sounds through the output device304, such as a monitor or speakers. The transceiver 314 is used toreceive and transmit wireless signals, delivering received signals tothe control circuit 306, and outputting signals generated by the controlcircuit 306 wirelessly. The communication device 300 in a wirelesscommunication system can also be utilized for realizing the AN 100 inFIG. 1 .

FIG. 4 is a simplified block diagram of the program code 312 shown inFIG. 3 in accordance with one embodiment of the invention. In thisembodiment, the program code 312 includes an application layer 400, aLayer 3 portion 402, and a Layer 2 portion 404, and is coupled to aLayer 1 portion 406. The Layer 3 portion 402 generally performs radioresource control. The Layer 2 portion 404 generally performs linkcontrol. The Layer 1 portion 406 generally performs physicalconnections.

3GPP TS 23.304 introduced the following:

4.3.9 5G ProSe UE-to-Network Relay

4.3.9.1 General

Both 5G ProSe Layer-2 and Layer-3 UE-to-Network Relay entity providesthe relaying functionality to support connectivity to the network for 5GProSe Remote UEs. It can be used for both public safety services andcommercial services (e.g. interactive service). Both 5G ProSe Layer-2and Layer-3 UE-to-Network Relay supports the following functions toenable connectivity to the network:

-   -   5G ProSe UE-to-Network Relay Discovery service as defined in        clause 6.3.2.3, to allow discovery by the 5G ProSe Remote UE;    -   access the 5GS as a UE as defined in TS 23.501 [4] with the        enhancements as specified in clauses 6.2 and 6.6;    -   relays unicast traffic (uplink and downlink) between the 5G        ProSe Remote UE and the network, supporting IP, Ethernet or        Unstructured traffic type.    -   NOTE: Relaying MBS traffic to a 5G ProSe Remote UE by a 5G ProSe        UE-to-Network Relay is not supported in this release of the        specification.        [ . . . ]        4.2.7.2 5G ProSe Layer-2 UE-to-Network Relay Reference        Architecture        FIG. 4.2.7.2-1 show the 5G ProSe Layer-2 UE-to-Network Relay        reference architecture. The 5G ProSe Layer-2 Remote UE and 5G        ProSe Layer-2 UE-to-Network Relay may be served by the same or        different PLMNs. If the serving PLMNs of the 5G ProSe Layer-2        Remote UE and the 5G ProSe Layer-2UE-to-Network Relay are        different then NG-RAN is shared by the serving PLMNs, see the 5G        MOCN architecture in clause 5.18 of TS 23.501 [4].

FIG. 4.2.7.2-1 of 3GPP TS 23.304 V17.0.0, Entitled “5G ProSe Layer-2UE-to-Network Relay Reference Architecture”, is Reproduced as FIG. 5

-   -   NOTE 1: Uu between the 5G ProSe Layer-2 Remote UE and NG-RAN        consists of RRC, SDAP and PDCP.    -   NOTE 2: The 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2        UE-to-Network Relay are served by the same NG-RAN. The Core        Network entities (e.g., AMF, SMF, UPF) serving the 5G ProSe        Layer-2 Remote UE and the 5G ProSe Layer-2 UE-to-Network Relay        can be the same or different.        [ . . . ]        6.1.1.7.2 5G ProSe Layer-2 UE-to-Network Relay The UE-UE        protocol stacks for discovery and PC5 signalling defined in        clause 6.1.1.2 apply to 5G ProSe Remote UE and 5G ProSe Layer-2        UE-to-Network Relay.        FIG. 6.1.1.7.2-1 illustrates the protocol stack of the NAS        connection for the 5G ProSe Layer-2 Remote UE for NAS-MM and        NAS-SM. The NAS messages are transparently transferred between        the 5G ProSe Layer-2 Remote UE and NG-RAN over the 5G ProSe        Layer-2 UE-to-Network Relay using:    -   PDCP end-to-end connection between the 5G ProSe Layer-2 Remote        UE and NG-RAN, where the role of the 5G ProSe Layer-2        UE-to-Network Relay is to relay the PDUs over the signalling        radio bear without any modifications and using the functionality        of the adaptation layer as specified in TS 38.351 [28].    -   Connection between NG-RAN and AMF over N2.    -   Connection between AMF and SMF over N11.

-   Editor's note: Whether the adaptation layer is supported over PC5    will be determined by RAN WG2.

FIG. 6.1.1.7.2-1 of 3GPP TS 23.304 V17.0.0, Entitled “End-to-End ControlPlane for a Remote UE Using Layer-2 UE-to-Network Relay”, is Reproducedas FIG. 6

The control plane protocol stack used by the 5G ProSe Layer-2UE-to-Network Relay is defined in clause 8.2.2 of TS 23.501 [4].

[ . . . ]

6.1.2.3.2 5G ProSe Layer-2 UE-to-Network Relay

FIG. 6.1.2.2.2-1 illustrates the protocol stack for the user planetransport, related to a PDU Session, including a 5G ProSe Layer 2UE-to-Network Relay. The PDU layer corresponds to the PDU carriedbetween the 5G ProSe Layer-2 Remote UE and the Data Network (DN) overthe PDU session. The SDAP and PDCP protocols are specified in TS 38.300[12]. PDCP end-to-end connection is between the 5G ProSe Layer-2 RemoteUE and NG-RAN. The functionality of the adaptation layer is specified inTS 38.351 [28].

-   Editor's note: Whether the adaptation layer is supported over PC5    will be determined by RAN WG2.

FIG. 6.1.2.3.2-1 of 3GPP TS 23.304 V17.0.0, Entitled “End-to-End UserPlane Stack for a 5G ProSe Remote UE Using 5G ProSe Layer-2UE-to-Network Relay”, is Reproduced as FIG. 7

[ . . . ]

6.4 5G ProSe Direct Communication

[ . . . ]

6.4.3 Unicast Mode 5G ProSe Direct Communication

6.4.3.1 Layer-2 Link Establishment Over PC5 Reference Point

To perform unicast mode of ProSe Direct communication over PC5 referencepoint, the UE is configured with the related information as described inclause 5.1.3.

FIG. 6.4.3.1-1 shows the layer-2 link establishment procedure for theunicast mode of ProSe Direct communication over PC5 reference point.

FIG. 6.4.3.1-1 of 3GPP TS 23.304 V17.0.0, Entitled “Layer-2 LinkEstablishment Procedure”, is Reproduced as FIG. 8

-   -   1. The UE(s) determine the destination Layer-2 ID for signalling        reception for PC5 unicast link establishment as specified in        clause 5.8.2.4.    -   2. The ProSe application layer in UE-1 provides application        information for PC5 unicast communication. The application        information includes the ProSe Service Info, UE's Application        Layer ID. The target UE's Application Layer ID may be included        in the application information.        -   The ProSe application layer in UE-1 may provide ProSe            Application Requirements for this unicast communication.            UE-1 determines the PC5 QoS parameters and PFI as specified            in clause 5.6.1.        -   If UE-1 decides to reuse the existing PC5 unicast link as            specified in clause 5.3.4, the UE triggers the Layer-2 link            modification procedure as specified in clause 6.4.3.4.    -   3. UE-1 sends a Direct Communication Request message to initiate        the unicast layer-2 link establishment procedure. The Direct        Communication Request message includes:        -   Source User Info: the initiating UE's Application Layer ID            (i.e. UE-Vs Application Layer ID).        -   If the ProSe application layer provided the target UE's            Application Layer ID in step 2, the following information is            included:            -   Target User Info: the target UE's Application Layer ID                (i.e. UE-2's Application Layer        -   ProSe Service Info: the information about the ProSe            identifier(s) requesting Layer-2 link establishment.        -   Security Information: the information for the establishment            of security.    -   NOTE 1: The Security Information and the necessary protection of        the Source User Info and Target User Info are defined by SA WG3.        -   The source Layer-2 ID and destination Layer-2 ID used to            send the Direct Communication Request message are determined            as specified in clauses 5.8.2.1 and 5.8.2.4. The destination            Layer-2 ID may be broadcast or unicast Layer-2 ID. When            unicast Layer-2 ID is used, the Target User Info shall be            included in the Direct Communication Request message.        -   UE-1 sends the Direct Communication Request message via PC5            broadcast or unicast using the source Layer-2 ID and the            destination Layer-2 ID.    -   4. Security with UE-1 is established as below:        -   4a. If the Target User Info is included in the Direct            Communication Request message, the target UE, i.e. UE-2,            responds by establishing the security with UE-1.        -   4b. If the Target User Info is not included in the Direct            Communication Request message, the UEs that are interested            in using the announced ProSe Service(s) over a PC5 unicast            link with UE-1 responds by establishing the security with            UE-1.    -   NOTE 2: The signalling for the Security Procedure is defined by        SA WG3. When the security protection is enabled, UE-1 sends the        following information to the target UE:        -   If IP communication is used:            -   IP Address Configuration: For IP communication, IP                address configuration is required for this link and                indicates one of the following values:                -   “DHCPv4 server” if only IPv4 address allocation                    mechanism is supported by the initiating UE, i.e.,                    acting as a DHCPv4 server; or                -   “IPv6 Router” if only IPv6 address allocation                    mechanism is supported by the initiating UE, i.e.,                    acting as an IPv6 Router; or                -   “DHCPv4 server & IPv6 Router” if both IPv4 and IPv6                    address allocation mechanism are supported by the                    initiating UE; or                -   “address allocation not supported” if neither IPv4                    nor IPv6 address allocation mechanism is supported                    by the initiating UE.            -   Link-Local IPv6 Address: a link-local IPv6 address                formed locally based on RFC 4862 [17] if UE-1 does not                support the IPv6 IP address allocation mechanism, i.e.                the IP Address Configuration indicates “address                allocation not supported”.        -   QoS Info: the information about PC5 QoS Flow(s). For each            PC5 QoS Flow, the PFI and the corresponding PC5 QoS            parameters (i.e. PQI and conditionally other parameters such            as MFBR/GFBR, etc.) and the associated ProSe identifier(s).        -   The source Layer-2 ID used for the security establishment            procedure is determined as specified in clauses 5.8.2.1 and            5.8.2.4. The destination Layer-2 ID is set to the source            Layer-2 ID of the received Direct Communication Request            message.        -   Upon receiving the security establishment procedure            messages, UE-1 obtains the peer UE's Layer-2 ID for future            communication, for signalling and data traffic for this            unicast link.    -   5. A Direct Communication Accept message is sent to UE-1 by the        target UE(s) that has successfully established security with        UE-1:        -   5a. (UE oriented Layer-2 link establishment) If the Target            User Info is included in the Direct Communication Request            message, the target UE, i.e. UE-2 responds with a Direct            Communication Accept message if the Application Layer ID for            UE-2 matches.        -   5b. (ProSe Service oriented Layer-2 link establishment) If            the Target User Info is not included in the Direct            Communication Request message, the UEs that are interested            in using the announced ProSe Service(s) respond to the            request by sending a Direct Communication Accept message            (UE-2 and UE-4 in FIG. 6.3.3.1-1).        -   The Direct Communication Accept message includes:            -   Source User Info: Application Layer ID of the UE sending                the Direct Communication Accept message.            -   QoS Info: the information about PC5 QoS Flow(s). For                each PC5 QoS Flow, the PFI and the corresponding PC5 QoS                parameters requested by UE-1 (i.e. PQI and conditionally                other parameters such as MFBR/GFBR, etc) and the                associated ProSe identifiers(s).            -   If IP communication is used:                -   IP Address Configuration: For IP communication, IP                    address configuration is required for this link and                    indicates one of the following values:                -    “DHCPv4 server” if only IPv4 address allocation                    mechanism is supported by the target UE, i.e.,                    acting as a DHCPv4 server; or                -    “IPv6 Router” if only IPv6 address allocation                    mechanism is supported by the target UE, i.e.,                    acting as an IPv6 Router; or                -    “DHCPv4 server & IPv6 Router” if both IPv4 and IPv6                    address allocation mechanism are supported by the                    target UE; or                -    “address allocation not supported” if neither IPv4                    nor IPv6 address allocation mechanism is supported                    by the target UE.            -   Link-Local IPv6 Address: a link-local IPv6 address                formed locally based on RFC 4862 [17] if the target UE                does not support the IPv6 IP address allocation                mechanism, i.e. the IP Address Configuration indicates                “address allocation not supported”, and UE-1 included a                link-local IPv6 address in the Direct Communication                Request message. The target UE shall include a                non-conflicting link-local IPv6 address.        -   If both UEs (i.e. the initiating UE and the target UE) are            selected to use link-local IPv6 address, they shall disable            the duplicate address detection defined in RFC 4862 [17].    -   NOTE 3: When either the initiating UE or the target UE indicates        the support of IPv6 routing, the corresponding address        configuration procedure would be carried out after the        establishment of the layer 2 link, and the link-local IPv6        addresses are ignored.        -   The ProSe layer of the UE that established PC5 unicast link            passes the PC5 Link Identifier assigned for the unicast link            and the PC5 unicast link related information down to the AS            layer. The PC5 unicast link related information includes            Layer-2 ID information (i.e. source Layer-2 ID and            destination Layer-2 ID). This enables the AS layer to            maintain the PC5 Link Identifier together with the PC5            unicast link related information.    -   6. ProSe data is transmitted over the established unicast link        as below:        -   The PC5 Link Identifier and PFI are provided to the AS            layer, together with the ProSe data. Optionally in addition,            the Layer-2 ID information (i.e. source Layer-2 ID and            destination Layer-2 ID) is provided to the AS layer.    -   NOTE 4: It is up to UE implementation to provide the Layer-2 ID        information to the AS layer. UE-1 sends the ProSe data using the        source Layer-2 ID (i.e. UE-Vs Layer-2 ID for this unicast link)        and the destination Layer-2 ID (i.e. the peer UE's Layer-2 ID        for this unicast link).    -   NOTE 5: PC5 unicast link is bi-directional, therefore the peer        UE of UE-1 can send the ProSe data to UE-1 over the unicast link        with UE-1.        [ . . . ]        6.4.3.6 Layer-2 Link Management Over PC5 Reference Point for 5G        ProSe UE-to-Network Relay        The Layer-2 link procedures over PC5 reference point for unicast        mode 5G ProSe Direct Communication as depicted from clause        6.4.3.1 to clause 6.4.3.5 can be used for the PC5 reference        point between 5G ProSe Remote UE and 5G ProSe UE-to-Network        Relay, with the following differences and clarifications:    -   The Layer-2 link modification procedure is applicable to ProSe        Communication via 5G ProSe Layer-3 UE-to-Network Relay, other        procedures are applicable to both ProSe Communication via 5G        ProSe Layer-2 UE-to-Network Relay and ProSe Communication via 5G        ProSe Layer-3 UE-to-Network Relay.

-   Editor's note: Whether the Layer-2 link modification procedure is    also applicable to ProSe Communication via 5G ProSe Layer-2    UE-to-Network Relay requires cooperation with RAN2.    -   The UE oriented Layer-2 link establishment is used with UE-1        representing the 5G ProSe Remote UE and UE-2 representing the 5G        ProSe UE-to-Network Relay. For other procedures either UE-1        represents the 5G ProSe Remote UE and UE-2 represents the 5G        ProSe UE-to-Network Relay, or UE-1 represents the 5G ProSe        UE-to-Network Relay and UE-2 represents the 5G ProSe Remote UE.        I.e. the Layer-2 link establishment is initiated by the 5G ProSe        Remote UE, while other procedures may be initiated either by the        5G ProSe Remote UE or by the 5G ProSe UE-to-Network Relay.        For the UE oriented Layer-2 link establishment as described in        the clause 6.4.3.1,    -   In step 1, the 5G ProSe Remote UE determines the destination        Layer-2 ID for PC5 unicast link establishment based on the        unicast source Layer-2 ID of the selected 5G ProSe UE-to-Network        relay (as specified in clause 5.8.3) during UE-to-Network Relay        discovery as specified in clause 6.3.2.3.    -   In step 2, 5G ProSe Remote UE (UE-1) determines the Relay        Service Code to be used. The Relay Service Code to be used is        selected from the received Relay Service Code(s) during        UE-to-Network Relay discovery as specified in clause 6.3.2.3.    -   In step 3, 5G ProSe Remote UE (UE-1) sends a unicast Direct        Communication Request message to the selected 5G ProSe        UE-to-Network Relay. The destination Layer-2 ID used to send the        Direct Communication Request message shall be unicast Layer-2 ID        as determined in step 1. The Direct Communication Request        message includes:    -   Source User Info: the identity of the Remote UE requesting relay        operation.        -   Target User Info: the identity of the UE-to-Network Relay            provided to the 5G ProSe Remote UE during UE-to-Network            Relay Discovery procedure.        -   Relay Service Code: indicates the connectivity service            provided by the 5G ProSe UE-to-Network Relay as requested by            the 5G ProSe Remote UE.        -   Security Information: the information for the establishment            of security.    -   In step 4 and step 5, step 4a and step 5a are performed if the        5G ProSe UE-to-Network Relay's identity matches the identity        provided in the Target User Info and the Relay Service Code is        one of the Relay Service Codes included during UE-to-Network        Relay discovery as specified in clause 6.3.2.3. The Source User        Info in the Direct Communication Accept message is the identity        of the UE-to-Network Relay. In case of 5G ProSe Layer-2        UE-to-Network Relay, the Remote UE does not send the IP Address        Configuration, Link-Local IPv6 Address and QoS Info to the 5G        ProSe Layer-2 UE-to-Network Relay, and the Direct Communication        Accept message does not include IP Address Configuration,        Link-Local IPv6 Address and QoS Info. In case of 5G ProSe        Layer-3 UE-to-Network Relay, the Direct Communication Accept        message does not include the IP Address Configuration indicating        the value “address allocation not supported”.    -   In case of 5G ProSe Layer-2 UE-to-Network Relay, step 6 is not        performed.        For the Layer-2 link release as described in the clause 6.4.3.3,    -   In step1, if the Layer-2 link release procedure is initiated by        the 5G ProSe UE-to-Network Relay, the Disconnect Request message        may indicate the 5G ProSe UE-to-Network Relay is temporarily not        available as described in clause 5.12.    -   NOTE: The form of the temporarily not available indication will        be determined by stage 3.    -   If the service authorization for acting as a 5G ProSe Remote UE        or as a 5G ProSe UE-to-Network Relay is revoked, the 5G ProSe        UE-to-Network Relay should initiate the release of the layer-2        link that the revoked authorization affects.        For the Layer-2 link modification as described in the clause        6.4.3.4,    -   In step1, the Layer-2 link modification procedure may be        initiated by the 5G ProSe Layer-3 Remote UE based on the        application information received from its ProSe application        layer. The Link Modification Request message may include the PC5        QoS Rule(s) for the PC5 QoS Flow(s) to be added or modified as        described in clause 5.6.2.1. The Layer-2 link modification        procedure may be initiated by the 5G ProSe Layer-3 UE-to-Network        Relay based on the information received from the SMF via NAS        signalling from SMF.        A 5G ProSe Remote UE and a 5G ProSe UE-to-Network Relay shall        set up a separate PC5 unicast links if an existing unicast        link(s) was established with a different Relay Service Code or        without a Relay Service Code.

3GPP TS 38.331 introduced the following:

5.2.2.3.3 Request for on Demand System Information

The UE shall:

-   -   1> if SIB1 includes si-SchedulingInfo containing        si-RequestConfigSUL and criteria to select supplementary uplink        as defined in TS 38.321[13], clause 5.1.1 is met:        -   [ . . . ]    -   1> else if SIB1 includes si-SchedulingInfo containing        si-RequestConfig and criteria to select normal uplink as defined        in TS 38.321[13], clause 5.1.1 is met:        -   [ . . . ]    -   1> else:        -   2> apply the default L1 parameter values as specified in            corresponding physical layer specifications except for the            parameters for which values are provided in SIB1;        -   2> apply the default MAC Cell Group configuration as            specified in 9.2.2;        -   2> apply the timeAlignmentTimerCommon included in SIB1;        -   2> apply the CCCH configuration as specified in 9.1.1.2;        -   2> initiate transmission of the RRCSystemInfoRequest message            in accordance with 5.2.2.3.4;        -   2> if acknowledgement for RRCSystemInfoRequest message is            received from lower layers:            -   3> acquire the requested SI message(s) as defined in                sub-clause 5.2.2.3.2, immediately;    -   1> if cell reselection occurs while waiting for the        acknowledgment for SI request from lower layers:        -   2> reset MAC;        -   2> if SI request is based on RRCSystemInfoRequest message:            -   3> release RLC entity for SRB0.                [ . . . ]                5.3.3 RRC Connection Establishment                5.3.3.1 General

FIG. 5.3.3.1-1 of 3GPP TS 38.331 V16.6.0, Entitled “RRC ConnectionEstablishment, Successful”, is Reproduced as FIG. 9

[ . . . ]

The purpose of this procedure is to establish an RRC connection. RRCconnection establishment involves SRB1 establishment. The procedure isalso used to transfer the initial NAS dedicated information/message fromthe UE to the network.

The network applies the procedure e.g. as follows:

-   -   When establishing an RRC connection;    -   When UE is resuming or re-establishing an RRC connection, and        the network is not able to retrieve or verify the UE context. In        this case, UE receives RRCSetup and responds with        RRCSetupComplete.        [ . . . ]        5.3.7 RRC Connection Re-Establishment        5.3.7.1 General

FIG. 5.3.7.1-1 of 3GPP TS 38.331 V16.6.0, Entitled “RRC ConnectionRe-Establishment, Successful”, is Reproduced as FIG. 10

[ . . . ]

The purpose of this procedure is to re-establish the RRC connection. AUE in RRC_CONNECTED, for which AS security has been activated with SRB2and at least one DRB setup or, for IAB, SRB2, may initiate the procedurein order to continue the RRC connection. The connection re-establishmentsucceeds if the network is able to find and verify a valid UE contextor, if the UE context cannot be retrieved, and the network responds withan RRCSetup according to clause 5.3.3.4.The network applies the procedure e.g as follows:

-   -   When AS security has been activated and the network retrieves or        verifies the UE context:        -   to re-activate AS security without changing algorithms;        -   to re-establish and resume the SRB1;    -   When UE is re-establishing an RRC connection, and the network is        not able to retrieve or verify the UE context:        -   to discard the stored AS Context and release all RBs and BH            RLC channels;        -   to fallback to establish a new RRC connection.            If AS security has not been activated, the UE shall not            initiate the procedure but instead moves to RRC_IDLE            directly, with release cause ‘other’. If AS security has            been activated, but SRB2 and at least one DRB or, for IAB,            SRB2, are not setup, the UE does not initiate the procedure            but instead moves to RRC_IDLE directly, with release cause            ‘RRC connection failure’.            5.3.7.2 Initiation            The UE initiates the procedure when one of the following            conditions is met:    -   1> upon detecting radio link failure of the MCG and t316 is not        configured, in accordance with 5.3.10; or    -   1> upon detecting radio link failure of the MCG while SCG        transmission is suspended, in accordance with 5.3.10; or    -   1> upon detecting radio link failure of the MCG while PSCell        change or PSCell addition is ongoing, in accordance with 5.3.10;        or    -   1> upon re-configuration with sync failure of the MCG, in        accordance with sub-clause 5.3.5.8.3; or    -   1> upon mobility from NR failure, in accordance with sub-clause        5.4.3.5; or    -   1> upon integrity check failure indication from lower layers        concerning SRB1 or SRB2, except if the integrity check failure        is detected on the RRCReestablishment message; or    -   1> upon an RRC connection reconfiguration failure, in accordance        with sub-clause 5.3.5.8.2; or    -   1> upon detecting radio link failure for the SCG while MCG        transmission is suspended, in accordance with subclause 5.3.10.3        in NR-DC or in accordance with TS 36.331 [10] subclause 5.3.11.3        in NE-DC; or    -   1> upon reconfiguration with sync failure of the SCG while MCG        transmission is suspended in accordance with subclause        5.3.5.8.3; or    -   1> upon SCG change failure while MCG transmission is suspended        in accordance with TS 36.331 [10] subclause 5.3.5.7a; or    -   1> upon SCG configuration failure while MCG transmission is        suspended in accordance with subclause 5.3.5.8.2 in NR-DC or in        accordance with TS 36.331 [10] subclause 5.3.5.5 in NE-DC; or    -   1> upon integrity check failure indication from SCG lower layers        concerning SRB3 while MCG is suspended; or    -   1> upon T316 expiry, in accordance with sub-clause 5.7.3b.5.        Upon initiation of the procedure, the UE shall:    -   1> stop timer T310, if running;    -   1> stop timer T312, if running;    -   1> stop timer T304, if running;    -   1> start timer T311;    -   1> stop timer T316, if running;    -   1> if UE is not configured with conditionalReconfiguration:        -   2> reset MAC;        -   2> release spCellConfig, if configured;        -   2> suspend all RBs, and BH RLC channels for IAB-MT, except            SRB0;        -   2> release the MCG SCell(s), if configured;        -   2> if MR-DC is configured:            -   3> perform MR-DC release, as specified in clause                5.3.5.10;        -   2> release delayBudgetReportingConfig, if configured and            stop timer T342, if running;        -   2> release overheatingAssistanceConfig, if configured and            stop timer T345, if running;        -   2> release idc-AssistanceConfig, if configured;        -   2> release btNameList, if configured;        -   2> release wlanNameList, if configured;        -   2> release sensorNameList, if configured;        -   2> release drx-PreferenceConfig for the MCG, if configured            and stop timer T346a associated with the MCG, if running;        -   2> release maxBW-PreferenceConfig for the MCG, if configured            and stop timer T346b associated with the MCG, if running;        -   2> release maxCC-PreferenceConfig for the MCG, if configured            and stop timer T346c associated with the MCG, if running;        -   2> release maxMIMO-LayerPreferenceConfig for the MCG, if            configured and stop timer T346d associated with the MCG, if            running;        -   2> release minSchedulingOffsetPreferenceConfig for the MCG,            if configured stop timer T346e associated with the MCG, if            running;        -   2> release releasePreferenceConfig, if configured stop timer            T346f, if running;        -   2> release onDemandSIB-Request if configured, and stop timer            T350, if running;        -   2> release referenceTimePreferenceReporting, if configured;        -   2> release sl-AssistanceConfigNR, if configured;        -   2> release obtain CommonLocation, if configured;    -   1> if any DAPS bearer is configured:        -   2> reset the source MAC and release the source MAC            configuration;        -   2> for each DAPS bearer:            -   3> release the RLC entity or entities as specified in TS                38.322 [4], clause 5.1.3, and the associated logical                channel for the source SpCell;            -   3> reconfigure the PDCP entity to release DAPS as                specified in TS 38.323 [5];        -   2> for each SRB:            -   3> release the PDCP entity for the source SpCell;            -   3> release the RLC entity as specified in TS 38.322 [4],                clause 5.1.3, and the associated logical channel for the                source SpCell;        -   2> release the physical channel configuration for the source            SpCell;        -   2> discard the keys used in the source SpCell (the K_(gNB)            key, the K_(RRCenc) key, the K_(RRCint) key, the K_(UPint)            key and the K_(UPenc) key), if any;    -   1> perform cell selection in accordance with the cell selection        process as specified in TS 38.304 [20].        5.3.7.3 Actions Following Cell Selection while T311 is Running        Upon selecting a suitable NR cell, the UE shall:    -   1> ensure having valid and up to date essential system        information as specified in clause 5.2.2.2;    -   1> stop timer T311;    -   1> if T390 is running:        -   2> stop timer T390 for all access categories;        -   2> perform the actions as specified in 5.3.14.4;    -   1> if the cell selection is triggered by detecting radio link        failure of the MCG or re-configuration with sync failure of the        MCG or mobility from NR failure, and    -   1> if attemptCondReconfig is configured; and    -   1> if the selected cell is one of the candidate cells for which        the reconfigurationWithSync is included in the masterCellGroup        in VarConditionalReconfig:        -   2> apply the stored condRRCReconfig associated to the            selected cell and perform actions as specified in 5.3.5.3;    -   NOTE 1: It is left to network implementation to how to avoid        keystream reuse in case of CHO based recovery after a failed        handover without key change.    -   1> else:        -   2> if UE is configured with conditionalReconfiguration:        -   3> reset MAC;        -   3> release spCellConfig, if configured;        -   3> release the MCG SCell(s), if configured;        -   3> release delayBudgetReportingConfig, if configured and            stop timer T342, if running;        -   3> release overheatingAssistanceConfig, if configured and            stop timer T345, if running;            -   3> if MR-DC is configured:                -   4> perform MR-DC release, as specified in clause                    5.3.5.10;            -   3> release idc-AssistanceConfig, if configured;            -   3> release btNameList, if configured;            -   3> release wlanNameList, if configured;            -   3> release sensorNameList, if configured;            -   3> release drx-PreferenceConfig for the MCG, if                configured and stop timer T346a associated with the MCG,                if running;            -   3> release maxBW-PreferenceConfig for the MCG, if                configured and stop timer T346b associated with the MCG,                if running;            -   3> release maxCC-PreferenceConfig for the MCG, if                configured and stop timer T346c associated with the MCG,                if running;            -   3> release maxMIMO-LayerPreferenceConfig for the MCG, if                configured and stop timer T346d associated with the MCG,                if running;            -   3> release minSchedulingOffsetPreferenceConfig for the                MCG, if configured and stop timer T346e associated with                the MCG, if running;            -   3> release releasePreferenceConfig, if configured and                stop timer T346f, if running;            -   3> release onDemandSIB-Request if configured, and stop                timer T350, if running;            -   3> release referenceTimePreferenceReporting, if                configured;            -   3> release sl-AssistanceConfigNR, if configured;            -   3> release obtain CommonLocation, if configured;            -   3> suspend all RBs, except SRB0;        -   2> remove all the entries within VarConditionalReconfig, if            any;        -   2> for each measId, if the associated reportConfig has a            reportType set to condTriggerConfig:            -   3> for the associated reportConfigId:                -   4> remove the entry with the matching reportConfigId                    from the reportConfigList within the VarMeasConfig;            -   3> if the associated measObjectId is only associated to                a reportConfig with reportType set to condTriggerConfig:                -   4> remove the entry with the matching measObjectId                    from the measObjectList within the VarMeasConfig;            -   3> remove the entry with the matching measId from the                measIdList within the VarMeasConfig;        -   2> start timer T301;        -   2> apply the default L1 parameter values as specified in            corresponding physical layer specifications except for the            parameters for which values are provided in SIB1;        -   2> apply the default MAC Cell Group configuration as            specified in 9.2.2;        -   2> apply the CCCH configuration as specified in 9.1.1.2;        -   2> apply the timeAlignmentTimerCommon included in SIB1;        -   2> initiate transmission of the RRCReestablishmentRequest            message in accordance with 5.3.7.4;    -   NOTE 2: This procedure applies also if the UE returns to the        source PCell. Upon selecting an inter-RAT cell, the UE shall:    -   1> perform the actions upon going to RRC_IDLE as specified in        5.3.11, with release cause ‘RRC connection failure’.        5.3.7.4 Actions Related to Transmission of        RRCReestablishmentRequest Message        The UE shall set the contents of RRCReestablishmentRequest        message as follows:    -   1> if the procedure was initiated due to radio link failure as        specified in 5.3.10.3 or reconfiguration with sync failure as        specified in 5.3.5.8.3:        -   2> set the reestablishmentCellId in the VarRLF-Report to the            global cell identity of the selected cell;    -   1> set the ue-Identity as follows:        -   2> set the c-RNTI to the C-RNTI used in the source PCell            (reconfiguration with sync or mobility from NR failure) or            used in the PCell in which the trigger for the            re-establishment occurred (other cases);        -   2> set the physCellId to the physical cell identity of the            source PCell (reconfiguration with sync or mobility from NR            failure) or of the PCell in which the trigger for the            re-establishment occurred (other cases);        -   2> set the shortMAC-I to the 16 least significant bits of            the MAC-I calculated:            -   3> over the ASN.1 encoded as per clause 8 (i.e., a                multiple of 8 bits) VarShortMAC-Input;            -   3> with the K_(RRCint) key and integrity protection                algorithm that was used in the source PCell                (reconfiguration with sync or mobility from NR failure)                or of the PCell in which the trigger for the                re-establishment occurred (other cases); and            -   3> with all input bits for COUNT, BEARER and DIRECTION                set to binary ones;    -   1> set the reestablishmentCause as follows:        -   2> if the re-establishment procedure was initiated due to            reconfiguration failure as specified in 5.3.5.8.2:            -   3> set the reestablishmentCause to the value                reconfigurationFailure;        -   2> else if the re-establishment procedure was initiated due            to reconfiguration with sync failure as specified in            5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT            mobility from NR failure):            -   3> set the reestablishmentCause to the value                handoverFailure;        -   2> else:            -   3> set the reestablishmentCause to the value                otherFailure;    -   1> re-establish PDCP for SRB1;    -   1> re-establish RLC for SRB1;    -   1> apply the default configuration defined in 9.2.1 for SRB1;    -   1> configure lower layers to suspend integrity protection and        ciphering for SRB1;    -   NOTE: Ciphering is not applied for the subsequent        RRCReestablishment message used to resume the connection. An        integrity check is performed by lower layers, but merely upon        request from RRC.    -   1> resume SRB1;    -   1> submit the RRCReestablishmentRequest message to lower layers        for transmission.        5.3.7.5 Reception of the RRCReestablishment by the UE        The UE shall:    -   1> stop timer T301;    -   1> consider the current cell to be the PCell;    -   1> store the nextHopChainingCount value indicated in the        RRCReestablishment message;    -   1> update the K_(gNB) key based on the current K_(gNB) key or        the NH, using the stored nextHopChainingCount value, as        specified in TS 33.501 [11];    -   1> derive the K_(RRCenc) and K_(UPenc) keys associated with the        previously configured cipheringAlgorithm, as specified in TS        33.501 [11];    -   1> derive the K_(RRCint) and K_(UPint) keys associated with the        previously configured integrityProtAlgorithm, as specified in TS        33.501 [11].    -   1> request lower layers to verify the integrity protection of        the RRCReestablishment message, using the previously configured        algorithm and the K_(RRCint) key;    -   1> if the integrity protection check of the RRCReestablishment        message fails:        -   2> perform the actions upon going to RRC_IDLE as specified            in 5.3.11, with release cause ‘RRC connection failure’, upon            which the procedure ends;    -   1> configure lower layers to resume integrity protection for        SRB1 using the previously configured algorithm and the        K_(RRCint) key immediately, i.e., integrity protection shall be        applied to all subsequent messages received and sent by the UE,        including the message used to indicate the successful completion        of the procedure;    -   1> configure lower layers to resume ciphering for SRB1 using the        previously configured algorithm and, the K_(RRCenc) key        immediately, i.e., ciphering shall be applied to all subsequent        messages received and sent by the UE, including the message used        to indicate the successful completion of the procedure;    -   1> release the measurement gap configuration indicated by the        measGapConfig, if configured;    -   1> set the content of RRCReestablishmentComplete message as        follows:        -   2> if the UE has logged measurements available for NR and if            the RPLMN is included in plmn-IdentityList stored in            VarLogMeasReport:            -   3> include the logMeasAvailable in the                RRCReestablishmentComplete message;            -   3> if Bluetooth measurement results are included in the                logged measurements the UE has available for NR:                -   4> include the logMeasAvailableBT in the                    RRCReestablishmentComplete message;            -   3> if WLAN measurement results are included in the                logged measurements the UE has available for NR:                -   4> include the logMeasAvailableWLAN in the                    RRCReestablishmentComplete message;        -   2> if the UE has connection establishment failure or            connection resume failure information available in            VarConnEstFailReport and if the RPLMN is equal to            plmn-Identity stored in VarConnEstFailReport:            -   3> include connEstFailInfoAvailable in the                RRCReestablishmentComplete message;        -   2> if the UE has radio link failure or handover failure            information available in VarRLF-Report and if the RPLMN is            included in plmn-IdentityList stored in VarRLF-Report; or        -   2> if the UE has radio link failure or handover failure            information available in VarRLF-Report of TS 36.331 [10] and            if the UE is capable of cross-RAT RLF reporting and if the            RPLMN is included in plmn-IdentityList stored in            VarRLF-Report of TS 36.331 [10]:            -   3> include rlf-InfoAvailable in the                RRCReestablishmentComplete message;    -   1> submit the RRCReestablishmentComplete message to lower layers        for transmission;    -   1> the procedure ends.        [ . . . ]        5.8.3 Sidelink UE Information for NR Sidelink Communication        5.8.3.1 General

FIG. 5.8.3.1-1 of 3GPP TS 38.331 V16.6.0, Entitled “Sidelink UEInformation for NR Sidelink Communication”, is Reproduced as FIG. 11

The purpose of this procedure is to inform the network that the UE:

-   -   is interested or no longer interested to receive or transmit NR        sidelink communication,    -   is requesting assignment or release of transmission resource for        NR sidelink communication,    -   is reporting QoS parameters and QoS profile(s) related to NR        sidelink communication,    -   is reporting that a sidelink radio link failure or sidelink RRC        reconfiguration failure has been detected,    -   is reporting the sidelink UE capability information of the        associated peer UE for unicast communication,    -   is reporting the RLC mode information of the sidelink data radio        bearer(s) received from the associated peer UE for unicast        communication.        5.8.3.2 Initiation        A UE capable of NR sidelink communication that is in        RRC_CONNECTED may initiate the procedure to indicate it is        (interested in) receiving or transmitting NR sidelink        communication in several cases including upon successful        connection establishment or resuming, upon change of interest,        upon changing QoS profiles, upon receiving        UECapabilityInformationSidelink from the associated peer UE,        upon RLC mode information updated from the associated peer UE or        upon change to a PCell providing SIB12 including        sl-ConfigCommonNR. A UE capable of NR sidelink communication may        initiate the procedure to request assignment of dedicated        sidelink DRB configuration and transmission resources for NR        sidelink communication transmission. A UE capable of NR sidelink        communication may initiate the procedure to report to the        network that a sidelink radio link failure or sidelink RRC        reconfiguration failure has been declared. Upon initiating this        procedure, the UE shall:    -   1> if SIB12 including sl-ConfigCommonNR is provided by the        PCell:        -   2> ensure having a valid version of SIB12 for the PCell;        -   2> if configured by upper layers to receive NR sidelink            communication on the frequency included in sl-FreqInfoList            in SIB12 of the PCell:            -   3> if the UE did not transmit a SidelinkUEInformationNR                message since last entering RRC_CONNECTED state; or            -   3> if since the last time the UE transmitted a                SidelinkUEInformationNR message the UE connected to a                PCell not providing SIB12 including sl-ConfigCommonNR;                or            -   3> if the last transmission of the                SidelinkUEInformationNR message did not include                sl-RxInterestedFreqList; or if the frequency configured                by upper layers to receive NR sidelink communication on                has changed since the last transmission of the                SidelinkUEInformationNR message:                -   4> initiate transmission of the                    SidelinkUEInformationNR message to indicate the NR                    sidelink communication reception frequency of                    interest in accordance with 5.8.3.3;        -   2> else:            -   3> if the last transmission of the                SidelinkUEInformationNR message included                sl-RxInterestedFreqList:                -   4> initiate transmission of the                    SidelinkUEInformationNR message to indicate it is no                    longer interested in NR sidelink communication                    reception in accordance with 5.8.3.3;        -   2> if configured by upper layers to transmit NR sidelink            communication on the frequency included in sl-FreqInfoList            in SIB12 of the PCell:            -   3> if the UE did not transmit a SidelinkUEInformationNR                message since last entering RRC_CONNECTED state; or            -   3> if since the last time the UE transmitted a                SidelinkUEInformationNR message the UE connected to a                PCell not providing SIB12 including sl-ConfigCommonNR;                or            -   3> if the last transmission of the                SidelinkUEInformationNR message did not include                sl-TxResourceReqList; or if the information carried by                the sl-TxResourceReqList has changed since the last                transmission of the SidelinkUEInformationNR message:                -   4> initiate transmission of the                    SidelinkUEInformationNR message to indicate the NR                    sidelink communication transmission resources                    required by the UE in accordance with 5.8.3.3;        -   2> else:            -   3> if the last transmission of the                SidelinkUEInformationNR message included                sl-TxResourceReqList:                -   4> initiate transmission of the                    SidelinkUEInformationNR message to indicate it no                    longer requires NR sidelink communication                    transmission resources in accordance with 5.8.3.3.                    5.8.3.3 Actions Related to Transmission of                    SidelinkUEInformationNR Message                    The UE shall set the contents of the                    SidelinkUEInformationNR message as follows:    -   1> if the UE initiates the procedure to indicate it is (no more)        interested to receive NR sidelink communication or to request        (configuration/release) of NR sidelink communication        transmission resources or to report to the network that a        sidelink radio link failure or sidelink RRC reconfiguration        failure has been declared (i.e. UE includes all concerned        information, irrespective of what triggered the procedure):        -   2> if SIB12 including sl-ConfigCommonNR is provided by the            PCell:            -   3> if configured by upper layers to receive NR sidelink                communication:                -   4> include sl-RxInterestedFreqList and set it to the                    frequency for NR sidelink communication reception;            -   3> if configured by upper layers to transmit NR sidelink                communication:                -   4> include sl-TxResourceReqList and set its fields                    (if needed) as follows for each destination for                    which it requests network to assign NR sidelink                    communication resource:                -    5> set sl-DestinationIdentity to the destination                    identity configured by upper layer for NR sidelink                    communication transmission;                -    5> set sl-CastType to the cast type of the                    associated destination identity configured by the                    upper layer for the NR sidelink communication                    transmission;                -    5> set sl-RLC-ModeIndication to include the RLC                    mode(s) and optionally QoS profile(s) of the                    sidelink QoS flow(s) of the associated RLC mode(s),                    if the associated bi-directional sidelink DRB has                    been established due to the configuration by                    RRCReconfigurationSidelink;                -    5> set sl-QoS-InfoList to include QoS profile(s) of                    the sidelink QoS flow(s) of the associated                    destination configured by the upper layer for the NR                    sidelink communication transmission;                -    5> set sl-InterestedFreqList to indicate the                    frequency of the associated destination for NR                    sidelink communication transmission;                -    5> set sl-TypeTxSyncList to the current                    synchronization reference type used on the                    associated sl-InterestedFreqList for NR sidelink                    communication transmission.                -    5> set sl-Ca pabilityInformationSidelink to include                    UECapabilityInformationSidelink message, if any,                    received from peer UE.                -   4> if a sidelink radio link failure or a sidelink                    RRC reconfiguration failure has been declared,                    according to clauses 5.8.9.3 and 5.8.9.1.8,                    respectively;                -    5> include sl-FailureList and set its fields as                    follows for each destination for which it reports                    the NR sidelink communication failure:                -    6> set sl-DestinationIdentity to the destination                    identity configured by upper layer for NR sidelink                    communication transmission;                -    6> if the sidelink RLF is detected as specified in                    sub-clause 5.8.9.3:                -    7> set sl-Failure as rlf for the associated                    destination for the NR sidelink communication                    transmission;                -    6> else if RRCReconfigurationFailureSidelink is                    received:                -   7> set sl-Failure as configFailure for the                    associated destination for the NR sidelink                    communication transmission;    -   1> if the UE initiates the procedure while connected to an        E-UTRA PCell:        -   2> submit the SidelinkUEInformationNR to lower layers via            SRB1, embedded in E-UTRA RRC message            ULInformationTransferIRAT as specified in TS 36.331 [10],            clause 5.6.28;    -   1> else:        -   2> submit the SidelinkUEInformationNR message to lower            layers for transmission.            [ . . . ]            5.8.9 Sidelink RRC Procedure            5.8.9.1 Sidelink RRC Reconfiguration            5.8.9.1.1 General

FIG. 5.8.9.1.1-1 of 3GPP TS 38.331 V16.6.0, Entitled “Sidelink RRCReconfiguration, Successful”, is Reproduced as FIG. 12

[ . . . ]

The purpose of this procedure is to modify a PC5-RRC connection, e.g. toestablish/modify/release sidelink DRBs, to (re-)configure NR sidelinkmeasurement and reporting, to (re-)configure sidelink CSI referencesignal resources and CSI reporting latency bound.The UE may initiate the sidelink RRC reconfiguration procedure andperform the operation in sub-clause 5.8.9.1.2 on the correspondingPC5-RRC connection in following cases:

-   -   the release of sidelink DRBs associated with the peer UE, as        specified in sub-clause 5.8.9.1a.1;    -   the establishment of sidelink DRBs associated with the peer UE,        as specified in sub-clause 5.8.9.1a.2;    -   the modification for the parameters included in SLRB-Config of        sidelink DRBs associated with the peer UE, as specified in        sub-clause 5.8.9.1a.2;    -   the (re-)configuration of the peer UE to perform NR sidelink        measurement and report.    -   the (re-)configuration of the sidelink CSI reference signal        resources and CSI reporting latency bound.        In RRC_CONNECTED, the UE applies the NR sidelink communications        parameters provided in RRCReconfiguration (if any). In RRC_IDLE        or RRC_INACTIVE, the UE applies the NR sidelink communications        parameters provided in system information (if any). For other        cases, UEs apply the NR sidelink communications parameters        provided in SidelinkPreconfigNR (if any). When UE performs state        transition between above three cases, the UE applies the NR        sidelink communications parameters provided in the new state,        after acquisition of the new configurations. Before acquisition        of the new configurations, UE continues applying the NR sidelink        communications parameters provided in the old state.        5.8.9.1.2 Actions Related to Transmission of        RRCReconfigurationSidelink Message        The UE shall set the contents of RRCReconfigurationSidelink        message as follows:    -   1> for each sidelink DRB that is to be released, according to        sub-clause 5.8.9.1a.1.1, due to configuration by        sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR or by upper        layers:        -   2> set the SLRB-PC5-ConfigIndex included in the            slrb-ConfigToReleaseList corresponding to the sidelink DRB;    -   1> for each sidelink DRB that is to be established or modified,        according to sub-clause 5.8.9.1a.2.1, due to receiving        sl-ConfigDedicatedNR, SIB12 or SidelinkPreconfigNR:        -   2> set the SLRB-Config included in the            slrb-ConfigToAddModList, according to the received            sl-RadioBearerConfig and sl-RLC-BearerConfig corresponding            to the sidelink DRB;    -   1> set the sl-MeasConfig as follows:        -   2> If the frequency used for NR sidelink communication is            included in sl-FreqInfoToAddModList in sl-ConfigDedicatedNR            within RRCReconfiguration message or included in            sl-ConfigCommonNR within SIB12:            -   3> if UE is in RRC_CONNECTED:                -   4> set the sl-MeasConfig according to stored NR                    sidelink measurement configuration information for                    this destination;            -   3> if UE is in RRC_IDLE or RRC_INACTIVE:                -   4> set the sl-MeasConfig according to stored NR                    sidelink measurement configuration received from                    SIB12;        -   2> else:            -   3> set the sl-MeasConfig according to the                sl-MeasPreconfig in SidelinkPreconfigNR;    -   1> start timer T400 for the destination associated with the        sidelink DRB;    -   1> set the sl-CSI-RS-Config;    -   1> set the sl-LatencyBoundCSI-Report,    -   NOTE 1: How to set the parameters included in sl-CSI-RS-Config        and sl-LatencyBoundCSI-Report is up to UE implementation.        The UE shall submit the RRCReconfigurationSidelink message to        lower layers for transmission.        5.8.9.1.3 Reception of an RRCReconfigurationSidelink by the UE        The UE shall perform the following actions upon reception of the        RRCReconfigurationSidelink:    -   1> if the RRCReconfigurationSidelink includes the        sl-ResetConfig:        -   2> perform the sidelink reset configuration procedure as            specified in 5.8.9.1.10;    -   1> if the RRCReconfigurationSidelink includes the        slrb-ConfigToReleaseList:        -   2> for each SLRB-PC5-ConfigIndex value included in the            slrb-ConfigToReleaseList that is part of the current UE            sidelink configuration;            -   3> perform the sidelink DRB release procedure, according                to sub-clause 5.8.9.1a.1;    -   1> if the RRCReconfigurationSidelink includes the        slrb-ConfigToAddModList:        -   2> for each slrb-PC5-ConfigIndex value included in the            slrb-ConfigToAddModList that is not part of the current UE            sidelink configuration:            -   3> if sl-MappedQoS-FlowsToAddList is included:                -   4> apply the SL-PQFI included in                    sl-MappedQoS-FlowsToAddList;            -   3> perform the sidelink DRB addition procedure,                according to sub-clause 5.8.9.1a.2;        -   2> for each slrb-PC5-ConfigIndex value included in the            slrb-ConfigToAddModList that is part of the current UE            sidelink configuration:            -   3> if sl-MappedQoS-FlowsToAddList is included:                -   4> add the SL-PQFI included in                    sl-MappedQoS-FlowsToAddList to the corresponding                    sidelink DRB;            -   3> if sl-MappedQoS-FlowsToReleaseList is included:                -   4> remove the SL-PQFI included in                    sl-MappedQoS-FlowsToReleaseList from the                    corresponding sidelink DRB;            -   3> if the sidelink DRB release conditions as described                in sub-clause 5.8.9.1a.1.1 are met:                -   4> perform the sidelink DRB release procedure                    according to sub-clause 5.8.9.1a.1.2;            -   3> else if the sidelink DRB modification conditions as                described in sub-clause 5.8.9.1a.2.1 are met:                -   4> perform the sidelink DRB modification procedure                    according to sub-clause 5.8.9.1a.2.2;    -   1> if the RRCReconfigurationSidelink message includes the        sl-MeasConfig:        -   2> perform the sidelink measurement configuration procedure            as specified in 5.8.10;    -   1> if the RRCReconfigurationSidelink message includes the        sl-CSI-RS-Config:        -   2> apply the sidelink CSI-RS configuration;    -   1> if the RRCReconfigurationSidelink message includes the        sl-LatencyBoundCSI-Report:        -   2> apply the configured sidelink CSI report latency bound;    -   1> if the UE is unable to comply with (part of) the        configuration included in the RRCReconfigurationSidelink (i.e.        sidelink RRC reconfiguration failure):        -   2> continue using the configuration used prior to the            reception of the RRCReconfigurationSidelink message;        -   2> set the content of the RRCReconfigurationFailureSidelink            message;            -   3> submit the RRCReconfigurationFailureSidelink message                to lower layers for transmission;    -   1> else:        -   2> set the content of the RRCReconfigurationCompleteSidelink            message;            -   3> submit the RRCReconfigurationCompleteSidelink message                to lower layers for transmission;    -   NOTE 1: When the same logical channel is configured with        different RLC mode by another UE, the UE handles the case as        sidelink RRC reconfiguration failure.        [ . . . ]        5.8.9.1a.3 Sidelink SRB Release        The UE shall:    -   1> if a PC5-RRC connection release for a specific destination is        requested by upper layers; or    -   1> if the sidelink radio link failure is detected for a specific        destination:        -   2> release the PDCP entity, RLC entity and the logical            channel of the sidelink SRB for PC5-RRC message of the            specific destination;        -   2> consider the PC5-RRC connection is released for the            destination.    -   1> if PC5-S transmission for a specific destination is        terminated in upper layers:        -   2> release the PDCP entity, RLC entity and the logical            channel of the sidelink SRB(s) for PC5-S message of the            specific destination;            5.8.9.1a.4 Sidelink SRB Addition            The UE shall:    -   1> if transmission of PC5-S message for a specific destination        is requested by upper layers for sidelink SRB:        -   2> establish PDCP entity, RLC entity and the logical channel            of a sidelink SRB for PC5-S message, as specified in            sub-clause 9.1.1.4;    -   1> if a PC5-RRC connection establishment for a specific        destination is indicated by upper layers:        -   2> establish PDCP entity, RLC entity and the logical channel            of a sidelink SRB for PC5-RRC message of the specific            destination, as specified in sub-clause 9.1.1.4;        -   2> consider the PC5-RRC connection is established for the            destination.            [ . . . ]            5.8.9.3 Sidelink Radio Link Failure Related Actions            The UE shall:    -   1> upon indication from sidelink RLC entity that the maximum        number of retransmissions for a specific destination has been        reached; or    -   1> upon T400 expiry for a specific destination; or    -   1> upon indication from MAC entity that the maximum number of        consecutive HARQ DTX for a specific destination has been        reached; or    -   1> upon integrity check failure indication from sidelink PDCP        entity concerning SL-SRB2 or SL-SRB3 for a specific destination:        -   2> consider sidelink radio link failure to be detected for            this destination;        -   2> release the DRBs of this destination, in according to            sub-clause 5.8.9.1a.1;        -   2> release the SRBs of this destination, in according to            sub-clause 5.8.9.1a.3;        -   2> discard the NR sidelink communication related            configuration of this destination;        -   2> reset the sidelink specific MAC of this destination;        -   2> consider the PC5-RRC connection is released for the            destination;        -   2> indicate the release of the PC5-RRC connection to the            upper layers for this destination (i.e. PC5 is unavailable);        -   2> if UE is in RRC_CONNECTED:            -   3> perform the sidelink UE information for NR sidelink                communication procedure, as specified in 5.8.3.3;    -   NOTE: It is up to UE implementation on whether and how to        indicate to upper layers to maintain the keep-alive procedure        [55].

A running CR of TS 38.331 introduced the following:

Next Modified Subclause

5.3.7 RRC Connection Re-Establishment

[ . . . ]

5.3.7.2 Initiation

The UE initiates the procedure when one of the following conditions ismet:

-   -   1> upon detecting radio link failure of the MCG and t316 is not        configured, in accordance with 5.3.10; or    -   1> upon detecting radio link failure of the MCG while SCG        transmission is suspended, in accordance with 5.3.10; or    -   1> upon detecting radio link failure of the MCG while PSCell        change or PSCell addition is ongoing, in accordance with 5.3.10;        or    -   1> upon re-configuration with sync failure of the MCG, in        accordance with sub-clause 5.3.5.8.3; or    -   1> upon mobility from NR failure, in accordance with sub-clause        5.4.3.5; or    -   1> upon integrity check failure indication from lower layers        concerning SRB1 or SRB2, except if the integrity check failure        is detected on the RRCReestablishment message; or    -   1> upon an RRC connection reconfiguration failure, in accordance        with sub-clause 5.3.5.8.2; or    -   1> upon detecting radio link failure for the SCG while MCG        transmission is suspended, in accordance with subclause 5.3.10.3        in NR-DC or in accordance with TS 36.331 [10] subclause 5.3.11.3        in NE-DC; or    -   1> upon reconfiguration with sync failure of the SCG while MCG        transmission is suspended in accordance with subclause        5.3.5.8.3; or    -   1> upon SCG change failure while MCG transmission is suspended        in accordance with TS 36.331 [10] subclause 5.3.5.7a; or    -   1> upon SCG configuration failure while MCG transmission is        suspended in accordance with subclause 5.3.5.8.2 in NR-DC or in        accordance with TS 36.331 [10] subclause 5.3.5.5 in NE-DC; or    -   1> upon integrity check failure indication from SCG lower layers        concerning SRB3 while MCG is suspended; or    -   1> upon T316 expiry, in accordance with sub-clause 5.7.3b.5; or    -   1> upon detecting sidelink radio link failure by L2 U2N Remote        UE in RRC_CONNECTED, in accordance with subclause 5.8.9.3.        Upon initiation of the procedure, the UE shall:    -   1> stop timer T310, if running;    -   1> stop timer T312, if running;    -   1> stop timer T304, if running;    -   1> start timer T311;    -   1> stop timer T316, if running;    -   1> if UE is not configured with conditionalReconfiguration:        -   2> reset MAC;        -   2> release spCellConfig, if configured;        -   2> suspend all RBs, and BH RLC channels for IAB-MT, except            SRB0;        -   2> release the MCG SCell(s), if configured;        -   2> if MR-DC is configured:            -   3> perform MR-DC release, as specified in clause                5.3.5.10;        -   2> release delayBudgetReportingConfig, if configured and            stop timer T342, if running;        -   2> release overheatingAssistanceConfig, if configured and            stop timer T345, if running;        -   2> release idc-AssistanceConfig, if configured;        -   2> release btNameList, if configured;        -   2> release wlanNameList, if configured;        -   2> release sensorNameList, if configured;        -   2> release drx-PreferenceConfig for the MCG, if configured            and stop timer T346a associated with the MCG, if running;        -   2> release maxBW-PreferenceConfig for the MCG, if configured            and stop timer T346b associated with the MCG, if running;        -   2> release maxCC-PreferenceConfig for the MCG, if configured            and stop timer T346c associated with the MCG, if running;        -   2> release maxMIMO-LayerPreferenceConfig for the MCG, if            configured and stop timer T346d associated with the MCG, if            running;        -   2> release minSchedulingOffsetPreferenceConfig for the MCG,            if configured stop timer T346e associated with the MCG, if            running;        -   2> release releasePreferenceConfig, if configured stop timer            T346f, if running;        -   2> release onDemandSIB-Request if configured, and stop timer            T350, if running;        -   2> release referenceTimePreferenceReporting, if configured;        -   2> release sl-AssistanceConfigNR, if configured;        -   2> release obtain CommonLocation, if configured;    -   1> if any DAPS bearer is configured:        -   2> reset the source MAC and release the source MAC            configuration;        -   2> for each DAPS bearer:            -   3> release the RLC entity or entities as specified in TS                38.322 [4], clause 5.1.3, and the associated logical                channel for the source SpCell;            -   3> reconfigure the PDCP entity to release DAPS as                specified in TS 38.323 [5];        -   2> for each SRB:            -   3> release the PDCP entity for the source SpCell;            -   3> release the RLC entity as specified in TS 38.322 [4],                clause 5.1.3, and the associated logical channel for the                source SpCell;        -   2> release the physical channel configuration for the source            SpCell;        -   2> discard the keys used in the source SpCell (the K_(gNB)            key, the K_(RRCenc) key, the K_(RRCint) key, the K_(UPint)            key and the K_(UPenc) key), if any;    -   1> if the UE connects with a L2 U2N Relay UE via PC5-RRC        connection (i.e. the UE is a L2 U2N Remote UE):    -   1> perform either cell selection in accordance with the cell        selection process as specified in TS 38.304 [20], or relay        selection as specified in clause 5.8.x3.3, or both;    -   1> else:        -   2> perform cell selection in accordance with the cell            selection process as specified in TS            [ . . . ]            5.3.7.3a Actions Following Relay Selection while [T311] is            Running            Upon selecting a suitable L2 U2N Relay UE, the L2 U2N Remote            UE shall:    -   1> ensure having valid and up to date essential system        information as specified in clause 5.2.2.2;    -   1> stop timer [T311];    -   1> if T390 is running:        -   2> stop timer T390 for all access categories;        -   2> perform the actions as specified in 5.3.14.4;    -   1> start timer [T301];    -   1> initiate the PC5 unicast link establishment as specified in        TS 23.304 [x1];    -   1> apply the specified configuration of SL-RLC0 as specified in        9.1.1.4;    -   1> initiate transmission of the RRCReestablishmentRequest        message in accordance with 5.3.7.4.        5.3.7.4 Actions Related to Transmission of        RRCReestablishmentRequest Message        The UE shall set the contents of RRCReestablishmentRequest        message as follows:    -   1> if the procedure was initiated due to radio link failure as        specified in 5.3.10.3 or reconfiguration with sync failure as        specified in 5.3.5.8.3:        -   2> set the reestablishmentCellId in the VarRLF-Report to the            global cell identity of the selected cell;    -   1> set the ue-Identity as follows:        -   2> set the c-RNTI to the C-RNTI used in the source PCell            (reconfiguration with sync or mobility from NR failure) or            used in the PCell in which the trigger for the            re-establishment occurred (other cases);        -   2> set the physCellId to the physical cell identity of the            source PCell (reconfiguration with sync or mobility from NR            failure) or of the PCell in which the trigger for the            re-establishment occurred (other cases);        -   2> set the shortMAC-I to the 16 least significant bits of            the MAC-I calculated:            -   3> over the ASN.1 encoded as per clause 8 (i.e., a                multiple of 8 bits) VarShortMAC-Input;            -   3> with the K_(RRCint) key and integrity protection                algorithm that was used in the source PCell                (reconfiguration with sync or mobility from NR failure)                or of the PCell in which the trigger for the                re-establishment occurred (other cases); and            -   3> with all input bits for COUNT, BEARER and DIRECTION                set to binary ones;    -   1> set the reestablishmentCause as follows:        -   2> if the re-establishment procedure was initiated due to            reconfiguration failure as specified in 5.3.5.8.2:            -   3> set the reestablishmentCause to the value                reconfigurationFailure;        -   2> else if the re-establishment procedure was initiated due            to reconfiguration with sync failure as specified in            5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT            mobility from NR failure):            -   3> set the reestablishmentCause to the value                handoverFailure;        -   2> else:            -   3> set the reestablishmentCause to the value                otherFailure;    -   1> re-establish PDCP for SRB1;    -   1> if the UE connects with a L2 U2N Relay UE via PC5-RRC        connection (i.e. the UE is a L2 U2N Remote UE):        -   2> apply the default configuration of SL-RLC1 as defined in            9.2.x for SRB1;    -   1> else:        -   2> re-establish RLC for SRB1;        -   2> apply the default configuration defined in 9.2.1 for            SRB1;    -   1> configure lower layers to suspend integrity protection and        ciphering for SRB1;    -   NOTE: Ciphering is not applied for the subsequent        RRCReestablishment message used to resume the connection. An        integrity check is performed by lower layers, but merely upon        request from RRC.    -   1> resume SRB1;    -   1> submit the RRCReestablishmentRequest message to lower layers        for transmission.

Next Modified Subclause

5.8.9 Sidelink RRC Procedure

5.8.9.1 Sidelink RRC Reconfiguration

5.8.9.1.1 General

[ . . . ]

The purpose of this procedure is to modify a PC5-RRC connection, e.g. toestablish/modify/release sidelink DRBs, to (re-)configure NR sidelinkmeasurement and reporting, to (re-)configure sidelink CSI referencesignal resources and CSI reporting latency bound.The UE may initiate the sidelink RRC reconfiguration procedure andperform the operation in sub-clause 5.8.9.1.2 on the correspondingPC5-RRC connection in following cases:

-   -   the release of sidelink DRBs associated with the peer UE, as        specified in sub-clause 5.8.9.1a.1;    -   the establishment of sidelink DRBs associated with the peer UE,        as specified in sub-clause 5.8.9.1a.2;    -   the modification for the parameters included in SLRB-Config of        sidelink DRBs associated with the peer UE, as specified in        sub-clause 5.8.9.1a.2;    -   the release of sidelink RLC bearers not associated with SL-PDCP        for L2 U2N Relay UE and Remote UE, as specified in sub-clause        5.8.9.x1.1;    -   the establishment of RLC bearers not associated with SL-PDCP for        L2 U2N Relay UE and Remote UE, as specified in sub-clause        5.8.9.x1.2;    -   the modification for the parameters included in        SL-RLC-BearerConfig of RLC bearers not associated with SL-PDCP        for L2 U2N Relay UE and Remote UE, as specified in sub-clause        5.8.9.x1.2;    -   the (re-)configuration of the peer UE to perform NR sidelink        measurement and report.    -   the (re-)configuration of the sidelink CSI reference signal        resources and CSI reporting latency bound.

In RRC_CONNECTED, the UE applies the NR sidelink communicationsparameters provided in RRCReconfiguration (if any). In RRC_IDLE orRRC_INACTIVE, the UE applies the NR sidelink communications parametersprovided in system information (if any). For other cases, UEs apply theNR sidelink communications parameters provided in SidelinkPreconfigNR(if any). When UE performs state transition between above three cases,the UE applies the NR sidelink communications parameters provided in thenew state, after acquisition of the new configurations. Beforeacquisition of the new configurations, UE continues applying the NRsidelink communications parameters provided in the old state.

Next Modified Subclause

5.8.9.3 Sidelink radio link failure related actions

The UE shall:

-   -   1> upon indication from sidelink RLC entity that the maximum        number of retransmissions for a specific destination has been        reached; or    -   1> upon T400 expiry for a specific destination; or    -   1> upon indication from MAC entity that the maximum number of        consecutive HARQ DTX for a specific destination has been        reached; or    -   1> upon integrity check failure indication from sidelink PDCP        entity concerning SL-SRB2 or SL-SRB3 for a specific destination:        -   2> consider sidelink radio link failure to be detected for            this destination;        -   2> release the DRBs of this destination, in according to            sub-clause 5.8.9.1a.1 if any;        -   2> release the SRBs of this destination, in according to            sub-clause 5.8.9.1a.3;        -   2> release the sidelink RLC bearers not associated with            SL-PDCP of this destination, in according to sub-clause            5.8.9.x1.1;        -   2> discard the NR sidelink communication related            configuration of this destination;        -   2> reset the sidelink specific MAC of this destination;        -   2> consider the PC5-RRC connection is released for the            destination;        -   2> indicate the release of the PC5-RRC connection to the            upper layers for this destination (i.e. PC5 is unavailable);        -   2> if UE is in RRC_CONNECTED:            -   3> perform the sidelink UE information for NR sidelink                communication procedure, as specified in 5.8.3.3;            -   3> if the UE connects with a L2 U2N Relay UE via PC5-RRC                connection (i.e. the UE is a L2 U2N Remote UE):                -   4> initiate the RRC connection re-establishment                    procedure as specified in 5.3.7.    -   NOTE: It is up to UE implementation on whether and how to        indicate to upper layers to maintain the keep-alive procedure        [55].

Next Modified Subclause(New)

5.8.9.x1 Sidelink RLC Bearer Management for L2 U2N Relay

5.8.9.x1.1 Sidelink RLC Bearer Release The UE shall:

-   -   1> for each sl-RLC-BearerConfigIndex included in the received        sl-RLC-BearerToReleaseList that is part of the current UE        sidelink configuration:        -   2> release the RLC entity and the corresponding logical            channel for NR sidelink communication, associated with the            sl-RLC-BearerConfigIndex;            5.8.9.x1.2 Sidelink RLC Bearer Addition/Modification            For each sl-RLC-BearerConfigIndex received in the            sl-RLC-BearerToAddModList IE the UE shall:    -   1> if the current configuration contains a sidelink RLC bearer        with the received sl-RLC-BearerConfigIndex:        -   2> reconfigure the sidelink RLC entity or entities in            accordance with the received sl-RLC-ConfigPC5;        -   2> reconfigure the sidelink logical channel in accordance            with the received sl-MAC-LogicalChannelConfigPC5;    -   1> else (a sidelink RLC bearer with the received        sl-RLC-BearerConfigIndex was not configured before):        -   2> establish an sidelink RLC entity in accordance with the            received sl-RLC-ConfigPC5;        -   2> configure the sidelink MAC entity with a logical channel            in accordance with the received            sl-MAC-LogicalChannelConfigPC5.

-   Editor's Note: RAN2 to further discuss whether new or existing PC-5    RRC message is used for RRC_IDLE/RRC_INACTIVE Remote UE to provide    5G-S-TMSI/I-RNTI as well as interested SIB type to Relay UE.

-   Editor's note: FFS how to capture the case of Relay UE in    RRC_CONNECTED for paging monitoring.

-   Editor's Note: RAN2 to further discuss whether new or existing PC-5    RRC message is used for SI forwarding.

Next Modified Subclause

9.1.1.4 SCCH Configuration

[ . . . ]

Parameters that are specified for NR sidelink L2 U2N Relay operations,which is used for the sidelink RLC channel for Remote UE's SRB0 messagetransmission. The sidelink RLC bearer using this configuration is namedas SL-RLC0.

Name Value Semantics description Ver RLC configurationAM >sn-FieldLength 12 >t-Reassembly Undefined Selected by the recevingUE, up to UE implementation >logicalChannelIdentity FFS MACconfiguration >priority  1 >proritisedBitRateInifinity >logicalChannelGroup  0

Next Modified Subclause

9.2.x Default Sidelink RLC Bearer Configuration

Parameters that are used for the sidelink RLC bearer for Remote UE'sSRB1 RRC message such as RRCResume and RRCReestablishment message. Thesidelink RLC bearer using this configuration is named as SL-RLC1.

Name Value Semantics description Ver RLC configurationAM >sn-FieldLength 12 >t-Reassembly Undefined Selected by the recevingUE, up to UE implementation >logicalChannelIdentity FFS MACconfiguration >priority  1 >proritisedBitRateInifinity >logicalChannelGroup  0

According to 3GPP TS 23.304, 5G ProSe Layer-2 UE-to-Network Relay isintroduced to provide the relaying functionality to support connectivityto the network for 5G ProSe Remote UEs. When a remote UE initiates aservice having traffic toward to network, the remote UE should establisha unicast link or a PC5-S connection with a relay UE. Basically, theremote UE could send a Direct Communication Request message forrequesting establishment of the unicast link to the relay UE with theremote UE's Layer 2 Identification (L2ID) as Source L2ID and the relayUE's L2ID as Destination L2ID. The relay UE can learn the remote UE'sL2ID by receiving the Direct Communication Request message with theremote UE's L2ID as Source L2ID. On the other hand, the remote UE couldestablish a first unicast link (for relaying) with the relay UE whilethe remote UE could establish a second unicast link (for non-relaying)with a non-relay UE.

According to 3GPP TS 38.331, a procedure for sendingSidelinkUEInformation message is introduced for UE to request gNB forassignment of transmission resource. For example, when UE1 establishes aunicast link with UE2 and UE1 is in RRC_CONNECTED, UE1 will send a firstSidelinkUEInformation message (including UE2's L2ID in destination list)to gNB. According to the first SidelinkUEInformation message, gNB maythen configure UE1 with PC5 AS configuration (e.g. Sidelink (SL) DataRadio Bearer (DRB) configuration, SL Service Data Adaptation Protocol(SDAP) configuration, SL RLC configuration, and/or etc.) for UE1 toperform sidelink communication with UE2.

3GPP TS 38.331 also introduces Sidelink RRC procedure for handlingSidelink Radio Link Failure (SL RLF) between two UEs (e.g. UE1 and UE2).That is, when UE1 detects SL RLF corresponding to UE2, UE1 will releasethe related PC5 transmission resources (including e.g. the SL DRBs, SLSRBs, etc.) and then indicate upper layer of UE1 that PC5 Radio ResourceControl (PC5-RRC) connection for UE2 is not available. Since UE2 is notavailable to UE1, UE1 could send a second SidelinkUEInformation messageto gNB for updating the destination list (e.g. exclude UE2's L2ID fromthe updated destination list) so that gNB can configure UE1 to releasethe related PC5 AS configuration.

In UE-to-Network (U2N) Relay, according to [3] the 3GPP email discussion[Post115-e][603][Relay] Relaying CR to 38.331 (“Draft_38331 Running CRfor SL relay_v14_rapp.docx”), if the remote UE detects SL RLF for anydestination while the remote UE in RRC_CONNECTED connects with the relayUE, the remote UE should firstly perform the Sidelink UE Informationprocedure and then initiate the RRC connection re-establishmentprocedure. In fact, the condition introduced in the 3GPP emaildiscussion [Post115-e][603][Relay] Relaying CR to 38.331 to trigger theRRC connection re-establishment procedure is also true if the remote UEdetects SL RLF on the non-relay UE (instead of the relay UE). In thissituation, the remote UE could incorrectly perform the RRC connectionre-establishment procedure due to the SL RLF on the non-relay UE sincethere is no problem on the RRC connection with gNB.

To address the issue, the remote UE could initiate or perform the RRCconnection re-establishment procedure (only) if/after/when/upon/in casethe destination for the SL RLF is the relay UE. Or, the remote UE could(only) initiate or perform the RRC connection re-establishment procedurein response to detection of SL RLF on the relay UE. The remote UE couldnot initiate or perform the RRC connection re-establishment procedureif/after/when/upon/in case the destination for the SL RLF is thenon-relay UE. Or, the remote UE could not initiate or perform the RRCconnection re-establishment procedure in response to detection of SL RLFon the non-relay UE.

On the other hand, according to the 3GPP email discussion[Post115-e][603][Relay] Relaying CR to 38.331, the remote UE couldgenerate a SidelinkUEInformation message (including destination list inwhich the relay UE's L2ID is removed) in the firstly performed SidelinkUE Information procedure. Since the remote UE may disconnect from therelay UE due to the SL RLF on the relay UE, the remote UE is not able tosend the SidelinkUEInformation message immediately. Thus, the remote UEcould buffer the SidelinkUEInformation message in lower layer of theremote UE.

Since the remote UE may select a new relay UE during the RRC connectionre-establishment procedure, after the RRC connection re-establishmentprocedure is completed, the remote UE still needs to send a newSidelinkUEInformation message (including destination list in which thenew relay UE's L2ID is included) to gNB via the new relay UE. In thissituation, the previously buffered SidelinkUEInformation message (notincluding the relay UE's L2ID) and the new SidelinkUEInformation message(not including the relay UE's L2ID but including the new relay UE'sL2ID) will be sent to gNB via the new relay UE. Actually, thetransmission of the previously buffered SidelinkUEInformation message isnot needed. To avoid the unnecessary transmission, the remote UE couldnot initiate or perform the Sidelink UE Information procedureif/after/when/upon/in case the destination for the SL RLF is the relayUE. Or, the remote UE could not initiate or perform the Sidelink UEInformation procedure in response to detection of SL RLF on the relayUE. The remote UE could still initiate or perform the Sidelink UEInformation procedure for other cases (e.g. the destination for the SLRLF is the non-relay UE).

Here are some potential text proposals:

Proposal 1

5.8.9.3 Sidelink Radio Link Failure Related Actions

The UE shall:

-   -   1> upon indication from sidelink RLC entity that the maximum        number of retransmissions for a specific destination has been        reached; or    -   1> upon T400 expiry for a specific destination; or    -   1> upon indication from MAC entity that the maximum number of        consecutive HARQ DTX for a specific destination has been        reached; or    -   1> upon integrity check failure indication from sidelink PDCP        entity concerning SL-SRB2 or SL-SRB3 for a specific destination:        -   2> consider sidelink radio link failure to be detected for            this destination;        -   2> release the DRBs of this destination, in according to            sub-clause 5.8.9.1a.1 if any;        -   2> release the SRBs of this destination, in according to            sub-clause 5.8.9.1a.3;        -   2> release the sidelink RLC bearers not associated with            SL-PDCP of this destination, in according to sub-clause            5.8.9.x1.1;        -   2> discard the NR sidelink communication related            configuration of this destination;        -   2> reset the sidelink specific MAC of this destination;        -   2> consider the PC5-RRC connection is released for the            destination;        -   2> indicate the release of the PC5-RRC connection to the            upper layers for this destination (i.e. PC5 is unavailable);        -   2> if UE is in RRC_CONNECTED:            -   3> perform the sidelink UE information for NR sidelink                communication procedure, as specified in 5.8.3.3;            -   3> if the destination for the sidelink radio link                failure is a L2 U2N Relay UE:                -   4> initiate the RRC connection re-establishment                    procedure as specified in 5.3.7.

Proposal 2

5.8.9.3 Sidelink Radio Link Failure Related Actions

The UE shall:

-   -   1> upon indication from sidelink RLC entity that the maximum        number of retransmissions for a specific destination has been        reached; or    -   1> upon T400 expiry for a specific destination; or    -   1> upon indication from MAC entity that the maximum number of        consecutive HARQ DTX for a specific destination has been        reached; or    -   1> upon integrity check failure indication from sidelink PDCP        entity concerning SL-SRB2 or SL-SRB3 for a specific destination:        -   2> consider sidelink radio link failure to be detected for            this destination;        -   2> release the DRBs of this destination, in according to            sub-clause 5.8.9.1a.1 if any;        -   2> release the SRBs of this destination, in according to            sub-clause 5.8.9.1a.3;        -   2> release the sidelink RLC bearers not associated with            SL-PDCP of this destination, in according to sub-clause            5.8.9.x1.1;        -   2> discard the NR sidelink communication related            configuration of this destination;        -   2> reset the sidelink specific MAC of this destination;        -   2> consider the PC5-RRC connection is released for the            destination;        -   2> indicate the release of the PC5-RRC connection to the            upper layers for this destination (i.e. PC5 is unavailable);        -   2> if UE is in RRC_CONNECTED:            -   3> if the destination for the sidelink radio link                failure is a L2 U2N Relay UE:                -   4> initiate the RRC connection re-establishment                    procedure as specified in 5.3.7.3> else:                -   4> perform the sidelink UE information for NR                    sidelink communication procedure, as specified in                    5.8.3.3.

FIG. 13 is a flow chart 1300 from the perspective of a remote UE. Instep 1305, the remote UE establishes a first unicast link with a relayUE. In step 1310, the remote UE establishes a RRC connection with anetwork node via the relay UE. In step 1315, the remote UE establishes asecond unicast link with a second UE. In step 1320, the remote UEdetects a sidelink radio link failure. In step 1325, the remote UEinitiates or performs a RRC connection re-establishment procedure if thesidelink radio link failure occurs on the first unicast link. In step1330, the remote UE initiates or performs a Sidelink UE Informationprocedure if the sidelink radio link failure occurs on the secondunicast link.

In one embodiment, the remote UE could initiate or perform no RRCconnection re-establishment procedure if the sidelink radio link failureoccurs on the second unicast link. The remote UE could initiate orperform no Sidelink UE Information procedure if the sidelink radio linkfailure occurs on the first unicast link.

In one embodiment, the first unicast link could be used for forwardingtraffic between the network node and the remote UE via the relay UE. Thenetwork node could be a base station or a gNB.

In one embodiment, the second unicast link could be used fortransferring traffic between the remote UE and the second UE. The secondUE could be a non-relay UE.

In one embodiment, the first unicast link could be associated with aProximity-based Services (ProSe) Relay Code. The second unicast link maynot be associated with any Proximity-based Services (ProSe) Relay Code.

Referring back to FIGS. 3 and 4 , in one exemplary embodiment of amethod for a remote UE, the remote UE 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the remote UE (i) to establish a first unicast link with a relayUE, (ii) to establish a RRC connection with a network node via the relayUE, (iii) to establish a second unicast link with a second UE, (iv) todetect a sidelink radio link failure, (v) to initiate or perform a RRCconnection re-establishment procedure if the sidelink radio link failureoccurs on the first unicast link, and (vi) to initiate or perform aSidelink UE Information procedure if the sidelink radio link failureoccurs on the second unicast link. Furthermore, the CPU 308 can executethe program code 312 to perform all of the above-described actions andsteps or others described herein.

FIG. 14 is a flow chart 1400 from the perspective of a remote UE. Instep 1405, the remote UE establishes a first unicast link with a relayUE. In step 1410, the remote UE establishes a RRC connection with anetwork node via the relay UE. In step 1415, the remote UE establishes asecond unicast link with a second UE. In step 1420, the remote UEdetects a sidelink radio link failure. In step 1425, the remote UEinitiates or performs a RRC connection re-establishment procedure if thesidelink radio link failure occurs on the first unicast link. In step1430, the remote UE initiates or performs no RRC connectionre-establishment procedure if the sidelink radio link failure occurs onthe second unicast link.

In one embodiment, the remote UE could initiate or perform a Sidelink UEInformation procedure if the sidelink radio link failure occurs on thesecond unicast link. The remote UE could initiate or perform no SidelinkUE Information procedure if the sidelink radio link failure occurs onthe first unicast link.

Referring back to FIGS. 3 and 4 , in one exemplary embodiment of amethod for a remote UE, the remote UE 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the remote UE (i) to establish a first unicast link with a relayUE, (ii) to establish a RRC connection with a network node via the relayUE, (iii) to establish a second unicast link with a second UE, (iv) todetect a sidelink radio link failure, (v) to initiate or perform a RRCconnection re-establishment procedure if the sidelink radio link failureoccurs on the first unicast link, and (vi) to initiate or perform no RRCconnection re-establishment procedure if the sidelink radio link failureoccurs on the second unicast link. Furthermore, the CPU 308 can executethe program code 312 to perform all of the above-described actions andsteps or others described herein.

FIG. 15 is a flow chart 1500 from the perspective of a remote UE. Instep 1505, the remote UE establishes a first unicast link with a relayUE. In step 1510, the remote UE establishes a RRC connection with anetwork node via the relay UE. In step 1515, the remote UE establishes asecond unicast link with a second UE. In step 1520, the remote UEdetects a sidelink radio link failure. In step 1525, the remote UEinitiates or performs a Sidelink UE Information procedure if thesidelink radio link failure occurs on the second unicast link. In step1525, the remote UE initiates or performs no Sidelink UE Informationprocedure if the sidelink radio link failure occurs on the first unicastlink.

In one embodiment, the remote UE could initiate or perform a RRCconnection re-establishment procedure if the sidelink radio link failureoccurs on the first unicast link. The remote UE could initiate orperform no RRC connection re-establishment procedure if the sidelinkradio link failure occurs on the second unicast link.

Referring back to FIGS. 3 and 4 , in one exemplary embodiment of amethod for a remote UE, the remote UE 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the remote UE (i) to establish a first unicast link with a relayUE, (ii) to establish a RRC connection with a network node via the relayUE, (iii) to establish a second unicast link with a second UE, (iv) todetect a sidelink radio link failure, (v) to initiate or perform aSidelink UE Information procedure if the sidelink radio link failureoccurs on the second unicast link, and (vi) to initiate or perform noSidelink UE Information procedure if the sidelink radio link failureoccurs on the first unicast link. Furthermore, the CPU 308 can executethe program code 312 to perform all of the above-described actions andsteps or others described herein.

In the context of the embodiments shown in FIGS. 14 and 15 and discussedabove, in one embodiment, the remote UE could transmit a first RRCmessage to the network node via the relay UE for request of establishingthe RRC connection. The remote UE could receive a second RRC messagefrom the first network node via the relay UE for establishing the RRCconnection. The remote UE could transmit a third RRC message to thefirst network node via the relay UE for completing establishment of theRRC connection.

In one embodiment, the network node could be a base station or a gNB.The first RRC message could be a RRCSetupRequest message. The second RRCmessage could be a RRCSetup message. The third RRC message could be aRRCSetupComplete message.

In one embodiment, the first unicast link could be associated with aProSe Relay Code. The second unicast link may not be associated with anyProSe Relay Code. The first unicast link could be used for forwardingtraffic between the network node and the remote UE via the relay UE. Thesecond unicast link could be used for transferring traffic between theremote UE and the second UE.

In one embodiment, the second UE could be a non-relay UE.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein could be embodied in a widevariety of forms and that any specific structure, function, or bothbeing disclosed herein is merely representative. Based on the teachingsherein one skilled in the art should appreciate that an aspect disclosedherein could be implemented independently of any other aspects and thattwo or more of these aspects could be combined in various ways. Forexample, an apparatus could be implemented or a method could bepracticed using any number of the aspects set forth herein. In addition,such an apparatus could be implemented or such a method could bepracticed using other structure, functionality, or structure andfunctionality in addition to or other than one or more of the aspectsset forth herein. As an example of some of the above concepts, in someaspects concurrent channels could be established based on pulserepetition frequencies. In some aspects concurrent channels could beestablished based on pulse position or offsets. In some aspectsconcurrent channels could be established based on time hoppingsequences. In some aspects concurrent channels could be establishedbased on pulse repetition frequencies, pulse positions or offsets, andtime hopping sequences.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a data memory such as RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codesrelating to one or more of the aspects of the disclosure. In someaspects a computer program product may comprise packaging materials.

While the invention has been described in connection with variousaspects, it will be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptation of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

The invention claimed is:
 1. A method for a remote User Equipment (UE), comprising: establishing a first unicast link with a relay UE; establishing a Radio Resource Control (RRC) connection with a network node via the relay UE; establishing a second unicast link with a second UE; detecting a sidelink radio link failure; initiating or performing a RRC connection re-establishment procedure in response to the sidelink radio link failure on the first unicast link, wherein the remote UE in the RRC connection re-establishment procedure performs a relay selection and/or a cell selection; and initiating or performing a Sidelink UE Information procedure in response to the sidelink radio link failure on the second unicast link, wherein the remote UE in the Sidelink UE Information procedure sends a Sidelink UE Information message to the network node to indicate the sidelink radio link failure on the second UE.
 2. The method of claim 1, further comprising: initiating or performing no RRC connection re-establishment procedure if the sidelink radio link failure occurs on the second unicast link.
 3. The method of claim 1, further comprising: initiating or performing no Sidelink UE Information procedure if the sidelink radio link failure occurs on the first unicast link.
 4. The method of claim 1, wherein the first unicast link is used for forwarding traffic between the network node and the remote UE via the relay UE.
 5. The method of claim 4, wherein the network node is a base station or a gNB.
 6. The method of claim 1, wherein the second unicast link is used for transferring traffic between the remote UE and the second UE.
 7. The method of claim 6, wherein the second UE is a non-relay UE.
 8. The method of claim 1, wherein the first unicast link is associated with a Proximity-based Services (ProSe) Relay Code.
 9. The method of claim 1, wherein the second unicast link is not associated with any Proximity-based Services (ProSe) Relay Code.
 10. A remote UE (User Equipment), comprising: a control circuit; a processor installed in the control circuit; and a memory installed in the control circuit and operatively coupled to the processor; wherein the processor is configured to execute a program code stored in the memory to: establish a first unicast link with a relay UE; establish a Radio Resource Control (RRC) connection with a network node via the relay UE; establish a second unicast link with a second UE; detect a sidelink radio link failure; initiate or perform a RRC connection re-establishment procedure in response to the sidelink radio link failure on the first unicast link, wherein the remote UE in the RRC connection re-establishment procedure performs a relay selection and/or a cell selection; and initiate or perform a Sidelink UE Information procedure in response to the sidelink radio link failure on the second unicast link, wherein the remote UE in the Sidelink UE Information procedure sends a Sidelink UE Information message to the network node to indicate the sidelink radio link failure on the second UE.
 11. The remote UE of claim 10, further comprising: initiating or performing no RRC connection re-establishment procedure if the sidelink radio link failure occurs on the second unicast link.
 12. The remote UE of claim 10, further comprising: initiating or performing no Sidelink UE Information procedure if the sidelink radio link failure occurs on the first unicast link.
 13. The remote UE of claim 10, wherein the first unicast link is used for forwarding traffic between the network node and the remote UE via the relay UE.
 14. The remote UE of claim 13, wherein the network node is a base station or a gNB.
 15. The remote UE of claim 10, wherein the second unicast link is used for transferring traffic between the remote UE and the second UE.
 16. The remote UE of claim 15, wherein the second UE is a non-relay UE.
 17. The remote UE of claim 10, wherein the first unicast link is associated with a Proximity-based Services (ProSe) Relay Code.
 18. The remote UE of claim 10, wherein the second unicast link is not associated with any Proximity-based Services (ProSe) Relay Code. 